The present invention relates to the field of wireless telecommunication. More specifically, the present invention relates to the field of the digital enhanced cordless telecommunications (DECT) system.
Within the field of wireless telecommunications systems there exists a system referred to as the digital enhanced cordless telecommunications (DECT) system. Within the DECT system, a user of a cordless portable telephone handset is able to communicate with a user of another telecommunication device by way of a fixed base station utilizing wireless communication. To enable the cordless telephone handset and the base station to communicate within the DECT system, a radio interface is utilized.
Specifically, the DECT standard describes a time division multiple access (TDMA) system for residential cordless telephone and data transmission applications. Furthermore, the DECT system provides a choice of 120 independent bidirectional communication channels, commonly referred to as DECT channels. It should be appreciated that the DECT channels are spread over 10 carrier radio frequencies, typically referred to as bearers. Thus, every bearer provides 12 independent DECT channels. During communication, one or more DECT channels are established between a mobile device (e.g., portable telephone handset) and a base station. In order to share the radio bearer among 12 potential subscribers, a TDMA mechanism is utilized to divide the bearer into 24 slots. More specifically, the first 12 slots are used for the downlink communication direction which is from the fixed base station to the portable telephone handset. Furthermore, the second 12 slots are used for the uplink communication direction which is from the portable telephone handset to the base station. It should be appreciated that the cycle to transmit the 24 slots is referred to as a DECT frame. The cycle time of the DECT frame is 10 milliseconds (ms). As such, the data transmission for the downlink direction as well as for the uplink direction on all 12 DECT channels are carried out within 10 ms. Moreover, every DECT channel offers a transmission capacity of up to 32 kilobits per second (kbits/s) in each direction. It should be noted that there are problems associated within the cordless communication of the DECT system.
One of the problems experienced within the DECT system is that the radio bearers are exposed to radio frequency (RF) noise and signal reflections from time to time. These disturbances lead to corrupted user data within the DECT channels on the receiver side. It should be appreciated that the quality criteria of the DECT standard is the rate of corrupted received user data in relation to correctly received user data. The object is to keep the bit error rate as low as possible in order to obtain a high throughput of correct user data over the DECT channels. Typically, corrupted user data degrades the voice quality (e.g., crackles) of telephony applications or the corrupted user data has to be retransmitted when used in data applications. Since corrupted user data of data applications will be retransmitted, the user data throughput is degraded over the DECT channel.
Specifically, when a prior art receiver device determines that a cyclic redundancy check (CRC) or other type of error detection mechanism within a received DECT data frame is not correct, the receiver typically discards the data frame and request a retransmission of that data frame from the transmitter. It should be appreciated that user data sent over a DECT channel is protected by a CRC, which is well known by those of ordinary skill in the art. It should be further appreciated that the retransmission procedure is repeated until the data frame has been retransmitted successfully or a retransmission counter exceeds a certain value. It is appreciated that there are no provisions within the DECT standard for selective retransmission of particular portions of the data frame. If the bad transmission condition persists, the portable telephone handset is free to move the DECT channel to another slot on the same radio bearer or to another radio bearer. However, as long as the DECT channel remains on the old slot, the throughput is seriously degraded due to the retransmissions of the data frame.
There is a prior art solution to decrease the bit error rate of data frames during communication transmission within the DECT system which uses a Reed Solomon Forward Error Correction scheme, which is well known by those of ordinary skill in the art. Basically, this scheme operates by storing the last 7 data frames received and then restores any corrupted data. There are disadvantages associated with this prior art solution. One of the main disadvantages of this scheme is that it is very computationally intensive and is typically realized within hardware. As such, it can be expensive to implement. Furthermore, another disadvantage of this prior art solution is that it introduces a certain amount of overhead within the protocol software to handle the retransmissions. Therefore, it is non-transparent to the DECT base stations and portable telephone handsets thereby resulting in modifications of them in order to operate properly. A further disadvantage of this prior art solution is that it introduces an additional system delay of about 70 ms. A system delay of this size typically excludes the use of this prior art solution with DECT system remote computer terminal applications or voice applications.
Accordingly, a need exists for a method and system for providing improved efficiency of retransmitted data frames within the DECT system. A further need exists for a method and system which meets the above need but is not expensive to implement. Still another need exists for a method and system which meets the above need and is transparent to the DECT base stations and portable appliances. Yet another need exists for a method and system which meets the above need and does not introduce a significant system delay to the receiving side within the DECT system.
The present invention provides a method and system for providing improved efficiency of retransmitted data frames within the digital enhanced cordless telecommunications (DECT) system. Furthermore, the present invention provides a method and system which achieves the above accomplishment and is inexpensive to implement. Moreover, the present invention provides a method and system which achieves the above accomplishment and is transparent to the DECT base stations and portable appliances. Additionally, the present invention provides a method and system which achieves the above accomplishment without introducing a significant system delay to the receiving side within the DECT system.
Specifically, one embodiment of the present invention includes a method for improving retransmission efficiency of a data frame within a communication system. The method includes the step of receiving and storing three corrupted versions of a data frame within a memory. Moreover, the method also includes the step of performing a byte-wise comparison of the three corrupted versions of the data frame to locate an inconsistent byte position. In response to locating the inconsistent byte position among the three corrupted versions of the data frame, the method includes the step of performing a byte-wise majority decision among the three corrupted versions of the data frame to select a correct byte value of the inconsistent byte position. Provided no correct byte value is selected by performing the byte-wise majority decision, the method also includes the step of performing a bit-wise comparison of the inconsistent byte position of the three corrupted versions of the data frame to locate an inconsistent bit position. In response to locating the inconsistent bit position among the inconsistent byte position of the three corrupted versions of the data frame, the method includes the step of performing a bit-wise majority decision to select a bit value of the inconsistent bit position.
In another embodiment, the present invention includes the steps of the above described embodiment, and further includes the step of constructing an output version of the data frame.
In still another embodiment, the present invention includes a communication device that includes a processor, an addressable data bus coupled to the processor, and a memory device coupled to communicate with the processor for performing a method for improving retransmission efficiency of a data frame within a communication system. The method includes the step of receiving and storing three corrupted versions of a data frame within a memory. Furthermore, the method includes the step of performing a byte-wise comparison of the three corrupted versions of the data frame to locate an inconsistent byte position. In response to locating the inconsistent byte position among the three corrupted versions of the data frame, the method includes the step of performing a byte-wise majority decision among the three corrupted versions of the data frame to select a correct byte value of the inconsistent byte position. Provided no correct byte value is selected by performing the byte-wise majority decision, the method includes the step of performing a bit-wise comparison of the inconsistent byte position of the three corrupted versions of the data frame to locate an inconsistent bit position. In response to locating the inconsistent bit position among the inconsistent byte position of the three corrupted versions of the data frame, the method includes the step of performing a bit-wise majority decision to select a bit value of the inconsistent bit position.
In yet another embodiment, the present invention includes the communication device described directly above, and the method further includes the step of constructing an output version of the data frame.
These and other advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the drawing figures.